With the advent of digital cinema and related electronic imaging opportunities, considerable attention has been directed to development of electronic projection apparatus. In order to provide a competitive alternative to conventional cinematic-quality film projectors, digital projection apparatus must meet high standards of performance, providing high resolution (2048×1080 pixels or higher), wide color gamut, high brightness (5000 lumens or greater), and frame-sequential contrast ratios exceeding 1,500:1.
Liquid-Crystal (LC) technology has been successfully harnessed to serve numerous display applications, ranging from monochrome alphanumeric display panels, to laptop computers, and even to large-scale full color displays. As is well known, an LC device forms an image as an array of pixels by selectively modulating the polarization state of incident light for each corresponding pixel. Continuing improvements of LC technology have yielded the benefits of lower cost, improved yields and reliability, and reduced power consumption and with steadily improved imaging characteristics, such as resolution, speed, and color.
While numerous different types of pixilated LC devices have been developed, any specific LC device is constructed according to one of two basic architectures:                The microdisplay architecture provides a pixel control structure that is based on high-density microlithography similar to that used for integrated circuit devices fabricated on semiconductor wafers. This includes LCOS (Liquid Crystal on Silicon) and HTPS (High Temperature Polysilicon) Transmissive LCDs, where the pixel structures are less than 50 um, typically on the order of 8-20 um.        The direct view TFT (Thin-Film Transistor) architecture, where the pixel control structure is formed on a transparent substrate, generally amorphous silicon (glass) and the pixel size is visible to the eye (approximately 50 um).        
In the first basic LC architecture, LCOS takes advantage of miniaturization and the utilization of microlithographic technologies to fabricate highly dense spatial light modulators in which the liquid crystal light-modulating material is sealed against the structured backplane of a silicon circuit. Essentially, LCOS fabrication combines LC design techniques with complementary metal-oxide semiconductor (CMOS) manufacturing processes.
LCOS LCDs appear to have some advantages as spatial light modulators for high-quality digital cinema projection systems. These advantages include a manageable device size (up to about 1.7″ diagonal), small gaps between pixels, and favorable device yields. Using LCOS technology, LC chips having imaging areas typically smaller than one square inch are capable of forming images having several million pixels. The relatively mature level of silicon etching technology has proved to be advantageous for the rapid development of LCOS devices exhibiting high speeds and excellent resolution. LCOS devices have been used as spatial light modulators in applications such as rear-projection television and business projection apparatus.
Referring to FIG. 1A, there is shown a simplified block diagram of a conventional electronic projection apparatus 10 using LCOS LCD devices. Each color path (r=Red, g=Green, b=Blue) uses similar components for forming a modulated light beam. Individual components within each path are labeled with an appended r, g, or b, appropriately. Following the red color path, a red light source 20r provides unmodulated light, which is conditioned by uniformizing optics 22r to provide a uniform illumination. A polarizing beamsplitter 24r directs light having the appropriate polarization state to a spatial light modulator 30r, which selectively modulates the polarization state of the incident red light over an array of pixel sites. The action of spatial light modulator 30r forms the red component of a full color image. The modulated light from this image, transmitted along an optical axis Or through polarizing beamsplitter 24r, is directed to a dichroic combiner 26, typically an X-cube or a Philips prism. Dichroic combiner 26 combines the red, green, and blue modulated images from separate optical axes Or/Og/Ob to form a combined, multicolor image for a projection lens 32 along a common optical axis O for projection onto a display surface 40, such as a projection screen. Optical paths for blue and green light modulation are similar. Green light from green light source 20g, conditioned by uniformizing optics 22g is directed through a polarizing beamsplitter 24g to a spatial light modulator 30g. The modulated light from this image, transmitted along an optical axis Og, is directed to dichroic combiner 26. Similarly, blue light from blue light source 20b, conditioned by uniformizing optics 22b is directed through a polarizing beamsplitter 24b to a spatial light modulator 30b. The modulated light from this image, transmitted along an optical axis Or, is directed to dichroic combiner 26.
Among examples of electronic projection apparatus that utilize LCOS LCD spatial light modulators with an arrangement similar to that of FIG. 1A are those disclosed in U.S. Pat. No. 5,808,795 (Shimomura et al.); U.S. Pat. No. 5,798,819 (Hattori et al.); U.S. Pat. No. 5,918,961 (Ueda); U.S. Pat. No. 6,010,221 (Maki et al.); U.S. Pat. No. 6,062,694 (Oikawa et al.); U.S. Pat. No. 6,113,239 (Sampsell et al.); and U.S. Pat. No. 6,231,192 (Konno et al.).
A related spatial light modulator LC technology that is similar in dimensional scale to that of LCOS devices is the transmissive LCD microdisplay. An example of this technology is the recently announced High-Temperature PolySilicon (HTPS) TFT device from Seiko Epson, a 2048×1080 pixel, 1.6″ diagonal device. The HTPS modulator is formed by lithographic etching on a quartz wafer, using methods similar to those followed for conventional LCOS device fabrication.
The second type of basic LC architecture, commonly used for laptop computers and larger display devices, is the so-called “direct view” LCD panel, in which a layer of liquid crystal is sandwiched between two sheets of glass or other transparent material. A backlighting assembly is utilized in conjunction with the panel. The backlighting assembly typically consists of an illumination source, such as either cold cathode florescent tubes or light emitting diodes, plus a series of optical components and optical films to improve the uniformity, polarization state, and angular distribution of the light delivered to the transmissive panel. Continuing improvement in Thin-Film Transistor (TFT) technology has proved beneficial for direct view LCD panels, allowing increasingly denser packing of transistors into an area of a single glass pane. In addition, new LC materials that enable thinner layers and faster response time have been developed. This, in turn, has helped to provide direct view LCD panels with improved resolution and increased speed. Thus, larger, faster LCD panels, having improved resolution and color, are being designed and utilized successfully for display imaging. These developments have been primarily directed to the goal of improved performance in the desktop monitor and home television marketplace.
As the above-cited patents show, developers of motion-picture quality projection apparatus have primarily directed their attention and energies to the first architecture, using LCOS LCD technology, rather than to the second architecture using TFT-based, direct view LC panels. There are a number of clearly obvious reasons for this. For example, the requirement for making projection apparatus as compact as possible argues for the deployment of miniaturized components, including miniaturized spatial light modulators, such as the LCOS LCDs, or other types of microdisplay devices, such as digital micromirror devices (DMDs). Its highly compact pixel arrangement, with pixels typically sized in the 8-20 micron range, allows a single LCOS LCD to provide sufficient resolution for a large projection screen, requiring an image in the range of 2048×1080 or 4096×2160 pixels, or better, as required by SMPTE (Society of Motion Picture and Television Engineers) specifications for Digital Cinema Projection. Other reasons for interest in LCOS LCDs over their direct-view LCD panel counterparts relates to performance attributes of currently available LCOS components, attributes such as response speeds of less than 4 ms, larger color gamut, and contrast ratios of 2000:1 and higher. In addition, reflective LCOS components allow higher power density when provided with heat-sinking, have an aperture ratio of above 70%, and typically don't employ color filter arrays or backlight units.
Yet another factor that tends to bias projector development efforts toward miniaturized devices relates to the dimensional characteristics of the film that is to be replaced. That is, the image-forming area of the LCOS LCD spatial light modulator, or its Digital Micromirror Device (DMD) counterpart, is comparable in size to the area of the image frame that is projected from the motion picture print film. This may somewhat simplify some of the projection optics design, including adapting existing designs from film-based imaging. However, this interest in LCOS LCD or DMD devices also results from an assumption on the part of designers that image formation at smaller dimensions would be most favorable. Thus, for conscious reasons, and in line with conventional reasoning and expectations, developers have assumed that the miniaturized LCOS LCD or DMD provides the most viable image-forming component for high-quality digital cinema projection.
While compact size and favorable response speeds are advantages offered by wafer-based LCD device architectures, these same devices have some inherent shortcomings that complicate their use in large-scale cinematic projection applications. One problem inherent with the use of miniaturized LCD and DMD spatial light modulators relates to brightness and efficiency. As is well known to those skilled in the imaging arts, any optical system is constrained by geometrical considerations, expressed in terms of etendue or, alternately, in terms of the Lagrange invariant, i.e., a product of the acceptance solid angle and the size of the aperture at any given plane in an optical system. Where systems are matched and symmetric, Lagrange and etendue are identical. In optical systems that are not matched or symmetric, the etendue is the smallest value that allows light through the system. (Refer to Polarization Engineering for LCD Projection, by Michael G. Robinson, Jianmin Chen, Gary D. Sharp, John Wiley & Sons Ltd, England, 2005, page 41.)
Etendue and the corollary, Lagrange invariant, provide a way to quantify an intuitive principle: only so much light can be provided from an area of a certain size. As the Lagrange invariant shows, when the emissive area is small, a large angle of emitted light is needed in order to achieve a certain level of brightness. Added complexity and cost result from the requirement to handle illumination at larger angles. This problem is noted and addressed for high-density LCOS devices in commonly assigned U.S. Pat. No. 6,758,565 entitled “Projection Apparatus Using Telecentric Optics” to Cobb et al.; U.S. Pat. No. 6,808,269 entitled “Projection Apparatus Using Spatial Light Modulator” to Cobb; and U.S. Pat. No. 6,676,260 entitled “Projection Apparatus Using Spatial Light Modulator with Relay Lens and Dichroic Combiner”, to Cobb et al. These patents disclose an electronic projection apparatus design using higher numerical apertures at the spatial light modulator for obtaining the necessary light, while reducing angular requirements elsewhere in the system.
Still other related problems with LCDs relate to the high angles of modulated light needed. The mechanism for image formation in LCD devices, and the inherent birefringence of the LCD itself, limit the contrast and color quality available from these devices when incident illumination is highly angular. In order to provide suitable levels of contrast, one or more compensator devices must often be used in an LCD system. This, however, further increases the complexity and cost of the projection system. An example of this is disclosed in commonly assigned U.S. Pat. No. 6,831,722 entitled, “Compensation Films for LCDs” to Ishikawa et al., which discloses the use of compensators for angular polarization effects of wiregrid polarizers and LCD devices. For these reasons, one should appreciate that microdisplay LCOS, HTPS LCD and DMD solutions face inherent limitations related to component size and light path geometry.
In addition to area and light angle considerations, a related consideration is that image-forming components also have limitations on energy density. With miniaturized spatial light modulators, and with LCDs in particular, only so much energy density can be tolerated at the component level. That is, a level of brightness beyond a certain threshold level can damage the device itself. Typically, energy density above about 15 W/cm2 would be excessive for an LCOS LCD with inorganic alignment layers. This, in turn, constrains the available brightness when using an LCOS LCD of 1.3 inch in diameter to no more than about 15,000 lumens. Heat build-up must also be prevented, since this would cause non-uniformity of the image and color aberrations, and could shorten the lifespan of the light modulator and its support components. For example, the behavior of absorptive polarization components used can be significantly compromised by heat build-up. This requires substantial cooling mechanisms for the spatial light modulator itself and careful engineering considerations for supporting optical components. Again, this adds cost and complexity to an optical system design.
Compounding this problem is the continuing trend toward further miniaturization in fabrication techniques for wafer devices, in order to obtain higher yields and improved manufacturing efficiency. It is apparent that the ongoing development of LCD spatial light modulators is following this same trend toward higher compactness and miniaturization. Light modulators near 0.5 in. diagonal have been developed, dramatically reducing the size of these devices from the 1.3 in. diagonal of earlier generation devices. However, considerations of etendue (or, similarly, Lagrange invariant) and energy density, as described earlier, show that further miniaturization will hamper the development of large-scale, theatre-quality projection apparatus using LCD devices, since it becomes increasingly more difficult to provide the needed brightness from smaller and smaller light-modulating devices. Yet another difficulty relates to relative defect size and fabrication yields. As pixels become increasingly smaller, such as in the 8-20 micron range, a small defect of only 1 or 2 microns in size can have a substantial affect on display quality. The same size defect on a device with larger pixels has correspondingly less impact on image quality.
In addition to etendue constraints, with any LC device, inherent constraints on aperture ratio must be considered. In general an aperture is provided for each pixel by a “black-matrix” pattern, in order to block incident light from negatively affecting the controlling transistor, which can be photosensitive, resulting in contrast loss. This aperture reduces the effective transmission of the device, resulting in an aperture ratio of 60% or less for HTPS LC devices, compared with approximately 90% for LCOS. With a substantially larger transmissive panel, and consequently, a larger pixel area, such a relatively small aperture ratio can still provide acceptable brightness. However, with the small pixel sizes of a microdisplay (such as the HTPS device), an aperture ratio this low is of a particular disadvantage. With respect to image quality, this aperture ratio may cause a visible “screen door” artifact when magnified to the display screen sizes required for typical theaters, that are around 40 feet wide or wider. Additionally, in micro-displays at the scale of the HTPS array, the device active area is still relatively small, and heat dissipation of this light absorbing aperture from an intense light source can further negatively affect the performance of the light modulator or the performance of its supporting optical components. Therefore, while this device type may be suitable for a digital projection application in a smaller venue, such as in a screening room or for business presentations, it does not appear to be capable enough for handling the amount of light required in typical cinema screen environments, where the average screen size generally requires a minimum of 10,000 lumens and where the largest of cinema display screens can require over 60,000 lumens. This high demand is well above what LCD micro-display devices (that is, both HTPS and LCOS devices with less than 2 inch diagonals) are able to provide at their physical limits, without taking exceptional measures for heat compensation and other factors that raise the potential cost of the projection system substantially.
Using conventional optical approaches in projector design, an illumination beam that is directed toward color separation and modulation components is concentrated so that it has as narrow a beam width as can be obtained. This strategy is preferred, because it allows favorable sizing of lenses, filters, polarizers, and other individual optical components and allows compact packaging of the overall optical system to condition, split, modulate, and recombine light. In the conventional LCOS embodiment of FIG. 1A, a narrow illumination beam is needed in order to concentrate light onto the small LCOS spatial light modulators themselves.
One significant limitation of conventional design approaches using LCOS devices, then, relates to brightness. As noted earlier with respect to the Lagrange invariant, only a certain amount of light can be obtained from a beam of a given width (that is, a given two-dimensional area) at narrow angles. Increasing the angle of the light beams decreases the image quality obtained when using dichroic separators and combiners, since dichroic coatings shift their spectral edges as a function of angle. Concentrating or expanding a light beam over any part of the optical path requires intervening lenses or other light-conditioning optical components. Thus, the task of contracting or expanding the illumination and modulated light beams in each color channel adds cost and complexity to the optical design. FIG. 1B shows an earlier embodiment in which the incident light angle is steep at the LCOS device to increase collection efficiency, but reduced before and after to decrease the spectral shift effects of the coatings, as well as the speed of the optical components. When applying conventional optical design practices to the problem, the design of an electronic color projection apparatus that provides high light output has been shown to be particularly challenging, since each additional optical component in the system tends to reduce light output and to introduce tradeoffs between image quality and light output. Conventional solutions constrain both the light output levels and overall image quality.
Low-end LCOS-based electronic projection designs have been successfully commercialized for home use in rear projection televisions delivering approximately 1000 lumens and for business presentation markets in which a modest amount of optical efficiency and brightness and reasonably good image quality at low cost are suitable. In order to meet the demands for higher brightness and improved image quality projector output that would be competitive with film-based projection apparatus, however, it appears that considerable tradeoffs must be made. To compensate for optical efficiencies of less than 10%, conventional LC-based electronic imaging apparatus must employ very bright light sources. For example the Sanyo PLVHD20, an HTPS LCD microdisplay projector with a 1.6″ diagonal Seiko-Epson LC chip, utilizes four 300 W UHP lamps, yet delivers only 7000 lumens. In this case, multiple lamps of lower wattage are used, to increase the output without enlarging the etendue as much as utilizing a single high wattage lamp, since the lamp arc gap grows in size (illumination etendue) faster than the available wattage. Similarly, the Sony SRX-R110 with 1.55″ LCOS microdisplays utilizes two more expensive 2.0 kW lamps to deliver 10,000 lumens. In both of these cases, lamp output is insufficiently matched to the LC spatial light modulator, with concomitant impact on heat, cost, and lamp lifetime. To withstand high energy density levels needed to optimize brightness, more costly components must be used in illumination and modulated light paths. For example, lower cost absorptive polarizers are supplanted by more costly wire grid polarizers in many designs. Thus, in an effort to obtain every available lumen at the output, conventional designs employ expensive, low reliability approaches that use either high-cost, high-performance optical components or multiples of lower cost, lower performance components.
In electronic projection apparatus, light of each component color, or spectral band, is separately modulated; then the modulated light of the component color channels is typically recombined to provide a full color image. Recombination of the modulated light can be performed directly on the projected surface when using separate projection optics in each color channel; alternately, modulated component colors can be recombined for projection from a single projection lens assembly. When recombining colors for a single projection lens assembly, one goal is to provide equal length optical paths in each color channel. Some conventional solutions for equalizing optical path lengths are given in U.S. Pat. No. 4,864,390 entitled, “Display System with Equal Path Lengths” to McKechnie et al. and in U.S. Pat. No. 6,431,709, entitled “Triple-Lens Type Projection Display with Uniform Optical Path Lengths for Different Color Components” to Tiao et al.
Given the substantial challenges in creating a high lumen projector utilizing micro-display LCD devices, such as HTPS and LCOS, creating a projector with large panel “direct view” type LC panels appears desirable. These “direct-view” LC panels have significantly improved their resolution, contrast and speed making them more of an alternative to micro-display than initially perceived. However, the “direct-view” panels as currently fabricated for use in flat panel applications, are not well suited for use in a high lumen projector. For example, the use of absorptive polarizers, which may be directly attached to TFT LCD panels, as these devices are commonly manufactured, is disadvantageous for image quality. Heat created from light absorption in these polarizers, which typically exceed about 20% of the light energy, causes consequent heating of the LCD materials, potentially resulting in a loss of contrast and contrast uniformity across the panel.
Similarly, high speed, high contrast LC panels dedicated for desktop monitors and televisions typically contain color filter arrays (CFA) inside the structure of the panel in order to provide the color performance required by these applications. These absorptive color filter arrays would not be suitable for use in a high lumen projector, again because heat absorption could result in non-uniform image artifacts and damage to the device. While high-resolution monochrome panels have been made for the medical industry, these panels typically have slow response times as they are often used for viewing still radiographic images. Newer panel technologies are being developed with faster responses times for improved video performance. Most significantly is a panel technology known as optically compensated bend mode (OCB) that offers speeds on the order of 2 ms. This mode is being pursued for the flat panel industry to allow field sequential color illumination offering a reduction in “direct view” backlighting cost and lower panel cost with the elimination of the expensive CFA. The OCB mode would be ideally suited for a high lumen digital projection system.
There have been various projection apparatus solutions proposed using the alternative direct view TFT LC panels. However, in most cases, these apparatus have been proposed for specialized applications, and are not intended for use in high-end digital cinema applications. For example, U.S. Pat. No. 5,889,614 (Cobben et al.) discloses the use of a TFT LC panel device as an image source for an overhead projection apparatus. U.S. Pat. No. 6,637,888 (Haven) discloses a rear screen TV display using a single subdivided TFT LC panel with Red, Green, and Blue color sources, using separate projection optics for each color path. Commonly assigned U.S. Pat. No. 6,505,940 (Gotham et al.) discloses a low-cost digital projector with a large-panel LC device encased in a kiosk arrangement to reduce vertical space requirements. While each of these examples employs a larger LC panel for image modulation, none of these designs is intended for motion picture projection at high resolution. Nor do the previous examples have sufficiently high brightness levels, or color comparable to that of conventional motion picture film, or acceptable contrast, or a high level of overall cinematic image quality. As a result, none of these proposed solutions would be suitable candidates for competing with conventional motion picture projection apparatus.
One attempt to provide a projection apparatus using TFT LC panels is disclosed in U.S. Pat. No. 5,758,940 entitled “Liquid Crystal Projection Display” to Ogino et al. In the Ogino et al. '940 apparatus, one or more Fresnel lenses is used to provide collimated illumination to the LC panel; another Fresnel lens then acts as a condenser to provide light to projection optics. Because it provides an imaging beam over a wide area, with a corrected illumination uniformity, the Ogino et al. '940 apparatus is advantaged for its relatively high light output, based on consideration of the Lagrange invariant described above. Notably, Ogino et al. '940 also describes using a single panel for modulation of all three primary colors, RGB (Red, Green, and Blue). For illumination of a monochrome LC panel, however, colors are provided in rapid sequence. This system would not produce color efficiently, nor would it modulate the successive color frames quickly enough to prevent motion artifacts. Therefore, while it may have some promise for TV sized projection apparatus and small-scale projectors, the proposed sequential color solution of the Ogino et al. '940 disclosure still falls short of the performance levels necessary for high-resolution projection systems that provide imaged light output having high intensity, at levels of 5,000 lumens and beyond.
Another recent attempt to utilize direct view TFT LC panels for projection for the command and control center marketplace is disclosed in U.S. Pat. No. 6,924,849 entitled, “Image Projection System With Multiple Arc Lamps and Flyseye Lens Array Light Homogenizer Directing Polychromatic Light on a Liquid Crystal Display” to Clifton et al. In the Clifton '849 apparatus, a 15″ TFT LC panel with color filters is used as the light modulator for a 67″ diagonal projection system. The solution proposed in the Clifton '849 disclosure is to increase brightness, without loss of contrast, by using combined multiple light sources, in an arrangement of reflective surfaces, to form a small effective light source. In the illumination portion of the Clifton '849 apparatus, light from multiple lamps is combined using a pinwheel mirror arrangement. This arrangement helps to illuminate the LC panel at low incident angles, nearly normal to the preferred LC optimum contrast direction, and thereby helps to improve the contrast ratio of the projection apparatus without the use of compensation films. The approach described in the '849 Clifton et al. patent also includes modifying the direct-view LCD panel for increased contrast, removing the wide view angle film that is conventionally provided with the panel. A further increase in contrast is claimed by redirecting the illumination through the LCD panel at an angle that is offset from normal to take advantage of inherent light modulation properties of the LC material. A Fresnel lens on the output light side of the LCD then compensates for the redirection of illumination on the input side of the LCD.
In spite of some considerable measures taken in the '849 Clifton solution, however, the efficiency of the resulting projector apparatus still remains relatively low. Moreover, while contrast may be improved in the apparatus of the '849 Clifton et al. disclosure, the apparatus still falls short of the brightness requirements for digital cinema projection. Significantly, the proposed solutions of the '849 Clifton et al. design fail to take advantage of increased etendue when using a large LC panel size. Some of the components of the proposed '849 Clifton et al. disclosure can adversely affect image quality. For example, the use of an output fresnel lens in front of the LC panel may be acceptable for the SXGA resolution levels of the apparatus described, but may cause significant contrast and image artifacts when utilized in a projection system with a minimum of 2048×1080 pixels and 5000 lumens. The use of lamps having arc gaps of up to 7 mm would not provide high efficiency, even where an LC panel of a 2-inch diagonal is used. The single panel color or monochrome configuration described in the '849 Clifton et al. patent would not be efficient with color light, whether using common absorptive color filter arrays that would cause problems in a high lumen system, or using sequential color that would cause motion artifacts. Additionally, continuing improvements in LCD panel design, including improved overall contrast ratio, may obviate the need for film removal to obtain high contrast or for illumination redirection solutions, both of which are proposed in the '849 Clifton et al. disclosure.
Thus, it can be seen that, although some digital cinema projection apparatus solutions have been predicated on the use of LCOS LCDs for image forming, there are inherent limitations in brightness and efficiency when using the miniaturized LCOS LCD components for this purpose. Direct view TFT LC panel solutions, on the other hand, because they do not have the same etendue-related limitations as do LCOS devices, have the potential to provide enhanced brightness levels over LCOS solutions. However, while projection apparatus using TFT LC panels have been disclosed, these have exhibited efficiency levels that are disappointing and have not been well suited to the demanding brightness levels combined with the additional requirements of contrast ratio, color uniformity, color gamut, and resolution as specified by the Society of Motion Picture and Television Engineers for certified digital cinema projectors.
The Society of Motion Picture and Television Engineers (SMPTE) is currently establishing a set of standards regarding certified digital cinema projection equipment. A consortium of motion picture studios, known as the Digital Cinema Initiative (DCI), created these baseline requirements. The DCI established stringent performance parameters that include contrast ratio, pixel resolution, light level at the screen, ANSI contrast, as well as color gamut and artifact allowance. These standards, in addition to the general competitive marketplace, require that a digital cinema projector have a sequential contrast on the order of 2000:1 with no color shifts, approximately 10,000 lumens or higher (for most screens), and a pixel count of 2048×1080 or 4096×2160.
The business of theatrical presentation of motion pictures is substantially different from that of projection in the home or conventional business environments. Traditionally theatres have built their business around the use of film, film projection equipment, and a revenue sharing stream in which different studios provide content to the theatre in return for a portion of the ticket sale price. The cost of the equipment to the theatre has been typically amortized over ten to thirty years, with few technology changes during this period. Servicing is minimal, with an occasional mechanical part failure, and periodic lamp replacement. Profits tend to be squeezed to the point where wattage of the projector lamp itself can be a significant cost factor that affects solvency.
Digital projection substantially changes this business model, but risks creating a somewhat more costly infrastructure for the theatrical venue. Conventional microdisplay-based projectors, built using costly, high-performance components, can cost as much as three times the cost of film projection equipment. Further, the life expectancy of modern digital projection equipment is unknown. Judging from the history of other benchmarks in the electronics industry such as digital television, computers, and telecommunication equipment, this lifetime can be less than that for conventional film projection apparatus, with a likely range from five to ten years. Planned obsolescence and component failure with conventional electronic projection apparatus raises profitability concerns. Without a significant gain in terms of cost effectiveness, light output, and optical efficiency, digital cinema may not be favorably poised to compete with film-based projection in the near future.
Thus, it can be seen that there is a need for a full-color projection apparatus of digital cinema performance levels that takes advantage of LC device technology at favorable cost, with increased optical efficiency, and overall light throughput.